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Add partial support for column-span property. #878

Merged
merged 4 commits into from Jul 3, 2019
Merged

Add partial support for column-span property. #878

merged 4 commits into from Jul 3, 2019

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@grewn0uille
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@grewn0uille grewn0uille commented Jun 4, 2019

Related to #719.

grewn0uille and others added 4 commits Jun 4, 2019
@liZe liZe marked this pull request as ready for review Jul 3, 2019
@liZe liZe merged commit e080d97 into master Jul 3, 2019
2 checks passed
@liZe liZe added this to the 48 milestone Jul 3, 2019
@liZe liZe deleted the column-span branch Jul 13, 2019
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this issue Oct 9, 2019
Version 50
----------

Released on 2019-09-19.

New features:

* `#209 <https://github.com/Kozea/WeasyPrint/issues/209>`_:
  Make ``break-*`` properties work inside tables
* `#661 <https://github.com/Kozea/WeasyPrint/issues/661>`_:
  Make blocks with ``overflow: auto`` grow to include floating children

Bug fixes:

* `#945 <https://github.com/Kozea/WeasyPrint/issues/945>`_:
  Don't break pages between a list item and its marker
* `#727 <https://github.com/Kozea/WeasyPrint/issues/727>`_:
  Avoid tables lost between pages
* `#831 <https://github.com/Kozea/WeasyPrint/issues/831>`_:
  Ignore auto margins on flex containers
* `#923 <https://github.com/Kozea/WeasyPrint/issues/923>`_:
  Fix a couple of crashes when splitting a line twice
* `#896 <https://github.com/Kozea/WeasyPrint/issues/896>`_:
  Fix skip stack order when using a reverse flex direction

Contributors:

- grewn0uille
- Guillaume Ayoub

Version 49
----------

Released on 2019-09-11.

Performance:

* Speed and memory use have been largely improved.

New features:

* `#700 <https://github.com/Kozea/WeasyPrint/issues/700>`_:
  Handle ``::marker`` pseudo-selector
* `135dc06c <https://github.com/Kozea/WeasyPrint/commit/135dc06c>`_:
  Handle ``recto`` and ``verso`` parameters for page breaks
* `#907 <https://github.com/Kozea/WeasyPrint/pull/907>`_:
  Provide a clean way to build layout contexts

Bug fixes:

* `#937 <https://github.com/Kozea/WeasyPrint/issues/937>`_:
  Fix rendering of tables with empty lines and rowspans
* `#897 <https://github.com/Kozea/WeasyPrint/issues/897>`_:
  Don't crash when small columns are wrapped in absolute blocks
* `#913 <https://github.com/Kozea/WeasyPrint/issues/913>`_:
  Fix a test about gradient colors
* `#924 <https://github.com/Kozea/WeasyPrint/pull/924>`_:
  Fix title for document with attachments
* `#917 <https://github.com/Kozea/WeasyPrint/issues/917>`_:
  Fix tests with Pango 1.44
* `#919 <https://github.com/Kozea/WeasyPrint/issues/919>`_:
  Fix padding and margin management for column flex boxes
* `#901 <https://github.com/Kozea/WeasyPrint/issues/901>`_:
  Fix width of replaced boxes with no intrinsic width
* `#906 <https://github.com/Kozea/WeasyPrint/issues/906>`_:
  Don't respect table cell width when content doesn't fit
* `#927 <https://github.com/Kozea/WeasyPrint/pull/927>`_:
  Don't use deprecated ``logger.warn`` anymore
* `a8662794 <https://github.com/Kozea/WeasyPrint/commit/a8662794>`_:
  Fix margin collapsing between caption and table wrapper
* `87d9e84f <https://github.com/Kozea/WeasyPrint/commit/87d9e84f>`_:
  Avoid infinite loops when rendering columns
* `789b80e6 <https://github.com/Kozea/WeasyPrint/commit/789b80e6>`_:
  Only use in flow children to set columns height
* `615e298a <https://github.com/Kozea/WeasyPrint/commit/615e298a>`_:
  Don't include floating elements each time we try to render a column
* `48d8632e <https://github.com/Kozea/WeasyPrint/commit/48d8632e>`_:
  Avoid not in flow children to compute column height
* `e7c452ce <https://github.com/Kozea/WeasyPrint/commit/e7c452ce>`_:
  Fix collapsing margins for columns
* `fb0887cf <https://github.com/Kozea/WeasyPrint/commit/fb0887cf>`_:
  Fix crash when using currentColor in gradients
* `f66df067 <https://github.com/Kozea/WeasyPrint/commit/f66df067>`_:
  Don't crash when using ex units in word-spacing in letter-spacing
* `c790ff20 <https://github.com/Kozea/WeasyPrint/commit/c790ff20>`_:
  Don't crash when properties needing base URL use var functions
* `d63eac31 <https://github.com/Kozea/WeasyPrint/commit/d63eac31>`_:
  Don't crash with object-fit: non images with no intrinsic size

Documentation:

* `#900 <https://github.com/Kozea/WeasyPrint/issues/900>`_:
  Add documentation about semantic versioning
* `#692 <https://github.com/Kozea/WeasyPrint/issues/692>`_:
  Add a snippet about PDF magnification
* `#899 <https://github.com/Kozea/WeasyPrint/pull/899>`_:
  Add .NET wrapper link
* `#893 <https://github.com/Kozea/WeasyPrint/pull/893>`_:
  Fixed wrong nested list comprehension example
* `#902 <https://github.com/Kozea/WeasyPrint/pull/902>`_:
  Add ``state`` to the ``make_bookmark_tree`` documentation
* `#921 <https://github.com/Kozea/WeasyPrint/pull/921>`_:
  Fix typos in the documentation
* `#328 <https://github.com/Kozea/WeasyPrint/issues/328>`_:
  Add CSS sample for forms

Contributors:

- grewn0uille
- Guillaume Ayoub
- Raphael Gaschignard
- Stani
- Szmen
- Thomas Dexter
- Tontyna

Version 48
----------

Released on 2019-07-08.

Dependencies:

* CairoSVG 2.4.0+ is now needed

New features:

* `#891 <https://github.com/Kozea/WeasyPrint/pull/891>`_:
  Handle ``text-overflow``
* `#878 <https://github.com/Kozea/WeasyPrint/pull/878>`_:
  Handle ``column-span``
* `#855 <https://github.com/Kozea/WeasyPrint/pull/855>`_:
  Handle all the ``text-decoration`` features
* `#238 <https://github.com/Kozea/WeasyPrint/issues/238>`_:
  Don't repeat background images when it's not needed
* `#875 <https://github.com/Kozea/WeasyPrint/issues/875>`_:
  Handle ``object-fit`` and ``object-position``
* `#870 <https://github.com/Kozea/WeasyPrint/issues/870>`_:
  Handle ``bookmark-state``

Bug fixes:

* `#686 <https://github.com/Kozea/WeasyPrint/issues/686>`_:
  Fix column balance when children are not inline
* `#885 <https://github.com/Kozea/WeasyPrint/issues/885>`_:
  Actually use the content box to resolve flex items percentages
* `#867 <https://github.com/Kozea/WeasyPrint/issues/867>`_:
  Fix rendering of KaTeX output, including (1) set row baseline of tables when
  no cells are baseline-aligned, (2) set baseline for inline tables, (3) don't
  align lines larger than their parents, (4) force CairoSVG to respect image
  size defined by CSS.
* `#873 <https://github.com/Kozea/WeasyPrint/issues/873>`_:
  Set a minimum height for empty list elements with outside marker
* `#811 <https://github.com/Kozea/WeasyPrint/issues/811>`_:
  Don't use translations to align flex items
* `#851 <https://github.com/Kozea/WeasyPrint/issues/851>`_,
  `#860 <https://github.com/Kozea/WeasyPrint/issues/860>`_:
  Don't cut pages when content overflows a very little bit
* `#862 <https://github.com/Kozea/WeasyPrint/issues/862>`_:
  Don't crash when using UTC dates in metadata

Documentation:

* `#854 <https://github.com/Kozea/WeasyPrint/issues/854>`_:
  Add a "Tips & Tricks" section

Contributors:

- Gabriel Corona
- Guillaume Ayoub
- Manuel Barkhau
- Nathan de Maestri
- grewn0uille
- theopeek

Version 47
----------

Released on 2019-04-12.

New features:

* `#843 <https://github.com/Kozea/WeasyPrint/pull/843>`_:
  Handle CSS variables
* `#846 <https://github.com/Kozea/WeasyPrint/pull/846>`_:
  Handle ``:nth()`` page selector
* `#847 <https://github.com/Kozea/WeasyPrint/pull/847>`_:
  Allow users to use a custom SSL context for HTTP requests

Bug fixes:

* `#797 <https://github.com/Kozea/WeasyPrint/issues/797>`_:
  Fix underlined justified text
* `#836 <https://github.com/Kozea/WeasyPrint/issues/836>`_:
  Fix crash when flex items are replaced boxes
* `#835 <https://github.com/Kozea/WeasyPrint/issues/835>`_:
  Fix ``margin-break: auto``

Version 46
----------

Released on 2019-03-20.

New features:

* `#771 <https://github.com/Kozea/WeasyPrint/issues/771>`_:
  Handle ``box-decoration-break``
* `#115 <https://github.com/Kozea/WeasyPrint/issues/115>`_:
  Handle ``margin-break``
* `#821 <https://github.com/Kozea/WeasyPrint/issues/821>`_:
  Continuous integration includes tests on Windows

Bug fixes:

* `#765 <https://github.com/Kozea/WeasyPrint/issues/765>`_,
  `#754 <https://github.com/Kozea/WeasyPrint/issues/754>`_,
  `#800 <https://github.com/Kozea/WeasyPrint/issues/800>`_:
  Fix many crashes related to the flex layout
* `#783 <https://github.com/Kozea/WeasyPrint/issues/783>`_:
  Fix a couple of crashes with strange texts
* `#827 <https://github.com/Kozea/WeasyPrint/pull/827>`_:
  Named strings and counters are case-sensitive
* `#823 <https://github.com/Kozea/WeasyPrint/pull/823>`_:
  Shrink min/max-height/width according to box-sizing
* `#728 <https://github.com/Kozea/WeasyPrint/issues/728>`_,
  `#171 <https://github.com/Kozea/WeasyPrint/issues/171>`_:
  Don't crash when fixed boxes are nested
* `#610 <https://github.com/Kozea/WeasyPrint/issues/610>`_,
  `#828 <https://github.com/Kozea/WeasyPrint/issues/828>`_:
  Don't crash when preformatted text lines end with a space
* `#808 <https://github.com/Kozea/WeasyPrint/issues/808>`_,
  `#387 <https://github.com/Kozea/WeasyPrint/issues/387>`_:
  Fix position of some images
* `#813 <https://github.com/Kozea/WeasyPrint/issues/813>`_:
  Don't crash when long preformatted text lines end with ``\n``

Documentation:

* `#815 <https://github.com/Kozea/WeasyPrint/pull/815>`_:
  Add documentation about custom ``url_fetcher``
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this issue Oct 18, 2019
Version 50
----------

Released on 2019-09-19.

New features:

* `#209 <https://github.com/Kozea/WeasyPrint/issues/209>`_:
  Make ``break-*`` properties work inside tables
* `#661 <https://github.com/Kozea/WeasyPrint/issues/661>`_:
  Make blocks with ``overflow: auto`` grow to include floating children

Bug fixes:

* `#945 <https://github.com/Kozea/WeasyPrint/issues/945>`_:
  Don't break pages between a list item and its marker
* `#727 <https://github.com/Kozea/WeasyPrint/issues/727>`_:
  Avoid tables lost between pages
* `#831 <https://github.com/Kozea/WeasyPrint/issues/831>`_:
  Ignore auto margins on flex containers
* `#923 <https://github.com/Kozea/WeasyPrint/issues/923>`_:
  Fix a couple of crashes when splitting a line twice
* `#896 <https://github.com/Kozea/WeasyPrint/issues/896>`_:
  Fix skip stack order when using a reverse flex direction

Contributors:

- grewn0uille
- Guillaume Ayoub

Version 49
----------

Released on 2019-09-11.

Performance:

* Speed and memory use have been largely improved.

New features:

* `#700 <https://github.com/Kozea/WeasyPrint/issues/700>`_:
  Handle ``::marker`` pseudo-selector
* `135dc06c <https://github.com/Kozea/WeasyPrint/commit/135dc06c>`_:
  Handle ``recto`` and ``verso`` parameters for page breaks
* `#907 <https://github.com/Kozea/WeasyPrint/pull/907>`_:
  Provide a clean way to build layout contexts

Bug fixes:

* `#937 <https://github.com/Kozea/WeasyPrint/issues/937>`_:
  Fix rendering of tables with empty lines and rowspans
* `#897 <https://github.com/Kozea/WeasyPrint/issues/897>`_:
  Don't crash when small columns are wrapped in absolute blocks
* `#913 <https://github.com/Kozea/WeasyPrint/issues/913>`_:
  Fix a test about gradient colors
* `#924 <https://github.com/Kozea/WeasyPrint/pull/924>`_:
  Fix title for document with attachments
* `#917 <https://github.com/Kozea/WeasyPrint/issues/917>`_:
  Fix tests with Pango 1.44
* `#919 <https://github.com/Kozea/WeasyPrint/issues/919>`_:
  Fix padding and margin management for column flex boxes
* `#901 <https://github.com/Kozea/WeasyPrint/issues/901>`_:
  Fix width of replaced boxes with no intrinsic width
* `#906 <https://github.com/Kozea/WeasyPrint/issues/906>`_:
  Don't respect table cell width when content doesn't fit
* `#927 <https://github.com/Kozea/WeasyPrint/pull/927>`_:
  Don't use deprecated ``logger.warn`` anymore
* `a8662794 <https://github.com/Kozea/WeasyPrint/commit/a8662794>`_:
  Fix margin collapsing between caption and table wrapper
* `87d9e84f <https://github.com/Kozea/WeasyPrint/commit/87d9e84f>`_:
  Avoid infinite loops when rendering columns
* `789b80e6 <https://github.com/Kozea/WeasyPrint/commit/789b80e6>`_:
  Only use in flow children to set columns height
* `615e298a <https://github.com/Kozea/WeasyPrint/commit/615e298a>`_:
  Don't include floating elements each time we try to render a column
* `48d8632e <https://github.com/Kozea/WeasyPrint/commit/48d8632e>`_:
  Avoid not in flow children to compute column height
* `e7c452ce <https://github.com/Kozea/WeasyPrint/commit/e7c452ce>`_:
  Fix collapsing margins for columns
* `fb0887cf <https://github.com/Kozea/WeasyPrint/commit/fb0887cf>`_:
  Fix crash when using currentColor in gradients
* `f66df067 <https://github.com/Kozea/WeasyPrint/commit/f66df067>`_:
  Don't crash when using ex units in word-spacing in letter-spacing
* `c790ff20 <https://github.com/Kozea/WeasyPrint/commit/c790ff20>`_:
  Don't crash when properties needing base URL use var functions
* `d63eac31 <https://github.com/Kozea/WeasyPrint/commit/d63eac31>`_:
  Don't crash with object-fit: non images with no intrinsic size

Documentation:

* `#900 <https://github.com/Kozea/WeasyPrint/issues/900>`_:
  Add documentation about semantic versioning
* `#692 <https://github.com/Kozea/WeasyPrint/issues/692>`_:
  Add a snippet about PDF magnification
* `#899 <https://github.com/Kozea/WeasyPrint/pull/899>`_:
  Add .NET wrapper link
* `#893 <https://github.com/Kozea/WeasyPrint/pull/893>`_:
  Fixed wrong nested list comprehension example
* `#902 <https://github.com/Kozea/WeasyPrint/pull/902>`_:
  Add ``state`` to the ``make_bookmark_tree`` documentation
* `#921 <https://github.com/Kozea/WeasyPrint/pull/921>`_:
  Fix typos in the documentation
* `#328 <https://github.com/Kozea/WeasyPrint/issues/328>`_:
  Add CSS sample for forms

Contributors:

- grewn0uille
- Guillaume Ayoub
- Raphael Gaschignard
- Stani
- Szmen
- Thomas Dexter
- Tontyna

Version 48
----------

Released on 2019-07-08.

Dependencies:

* CairoSVG 2.4.0+ is now needed

New features:

* `#891 <https://github.com/Kozea/WeasyPrint/pull/891>`_:
  Handle ``text-overflow``
* `#878 <https://github.com/Kozea/WeasyPrint/pull/878>`_:
  Handle ``column-span``
* `#855 <https://github.com/Kozea/WeasyPrint/pull/855>`_:
  Handle all the ``text-decoration`` features
* `#238 <https://github.com/Kozea/WeasyPrint/issues/238>`_:
  Don't repeat background images when it's not needed
* `#875 <https://github.com/Kozea/WeasyPrint/issues/875>`_:
  Handle ``object-fit`` and ``object-position``
* `#870 <https://github.com/Kozea/WeasyPrint/issues/870>`_:
  Handle ``bookmark-state``

Bug fixes:

* `#686 <https://github.com/Kozea/WeasyPrint/issues/686>`_:
  Fix column balance when children are not inline
* `#885 <https://github.com/Kozea/WeasyPrint/issues/885>`_:
  Actually use the content box to resolve flex items percentages
* `#867 <https://github.com/Kozea/WeasyPrint/issues/867>`_:
  Fix rendering of KaTeX output, including (1) set row baseline of tables when
  no cells are baseline-aligned, (2) set baseline for inline tables, (3) don't
  align lines larger than their parents, (4) force CairoSVG to respect image
  size defined by CSS.
* `#873 <https://github.com/Kozea/WeasyPrint/issues/873>`_:
  Set a minimum height for empty list elements with outside marker
* `#811 <https://github.com/Kozea/WeasyPrint/issues/811>`_:
  Don't use translations to align flex items
* `#851 <https://github.com/Kozea/WeasyPrint/issues/851>`_,
  `#860 <https://github.com/Kozea/WeasyPrint/issues/860>`_:
  Don't cut pages when content overflows a very little bit
* `#862 <https://github.com/Kozea/WeasyPrint/issues/862>`_:
  Don't crash when using UTC dates in metadata

Documentation:

* `#854 <https://github.com/Kozea/WeasyPrint/issues/854>`_:
  Add a "Tips & Tricks" section

Contributors:

- Gabriel Corona
- Guillaume Ayoub
- Manuel Barkhau
- Nathan de Maestri
- grewn0uille
- theopeek

Version 47
----------

Released on 2019-04-12.

New features:

* `#843 <https://github.com/Kozea/WeasyPrint/pull/843>`_:
  Handle CSS variables
* `#846 <https://github.com/Kozea/WeasyPrint/pull/846>`_:
  Handle ``:nth()`` page selector
* `#847 <https://github.com/Kozea/WeasyPrint/pull/847>`_:
  Allow users to use a custom SSL context for HTTP requests

Bug fixes:

* `#797 <https://github.com/Kozea/WeasyPrint/issues/797>`_:
  Fix underlined justified text
* `#836 <https://github.com/Kozea/WeasyPrint/issues/836>`_:
  Fix crash when flex items are replaced boxes
* `#835 <https://github.com/Kozea/WeasyPrint/issues/835>`_:
  Fix ``margin-break: auto``

Version 46
----------

Released on 2019-03-20.

New features:

* `#771 <https://github.com/Kozea/WeasyPrint/issues/771>`_:
  Handle ``box-decoration-break``
* `#115 <https://github.com/Kozea/WeasyPrint/issues/115>`_:
  Handle ``margin-break``
* `#821 <https://github.com/Kozea/WeasyPrint/issues/821>`_:
  Continuous integration includes tests on Windows

Bug fixes:

* `#765 <https://github.com/Kozea/WeasyPrint/issues/765>`_,
  `#754 <https://github.com/Kozea/WeasyPrint/issues/754>`_,
  `#800 <https://github.com/Kozea/WeasyPrint/issues/800>`_:
  Fix many crashes related to the flex layout
* `#783 <https://github.com/Kozea/WeasyPrint/issues/783>`_:
  Fix a couple of crashes with strange texts
* `#827 <https://github.com/Kozea/WeasyPrint/pull/827>`_:
  Named strings and counters are case-sensitive
* `#823 <https://github.com/Kozea/WeasyPrint/pull/823>`_:
  Shrink min/max-height/width according to box-sizing
* `#728 <https://github.com/Kozea/WeasyPrint/issues/728>`_,
  `#171 <https://github.com/Kozea/WeasyPrint/issues/171>`_:
  Don't crash when fixed boxes are nested
* `#610 <https://github.com/Kozea/WeasyPrint/issues/610>`_,
  `#828 <https://github.com/Kozea/WeasyPrint/issues/828>`_:
  Don't crash when preformatted text lines end with a space
* `#808 <https://github.com/Kozea/WeasyPrint/issues/808>`_,
  `#387 <https://github.com/Kozea/WeasyPrint/issues/387>`_:
  Fix position of some images
* `#813 <https://github.com/Kozea/WeasyPrint/issues/813>`_:
  Don't crash when long preformatted text lines end with ``\n``

Documentation:

* `#815 <https://github.com/Kozea/WeasyPrint/pull/815>`_:
  Add documentation about custom ``url_fetcher``
@JohannesMunk
Copy link

@JohannesMunk JohannesMunk commented Sep 4, 2020

Hey liZe!

This new balancing algorithm is the cause of quite a big slowdown in document generation in our projects. We have several documents with colspans>=2 that span multiple pages and contain complex block stuff. Rendering all columns content on every pixel the height is increased was getting to slow. 90mins for 230 pages..

While keeping the basic idea alive instead of a linear scan to find the smallest columns height for a "balanced" layout I implemented a simple binary search.

    # Balance.
    #
    # The current algorithm starts from the ideal height (the total height
    # divided by the number of columns). We then iterate until the last column
    # is not the highest one. At the end of each loop, we add the minimal
    # height needed to make one direct child at the top of one column go to the
    # end of the previous column.
    #
    # We rely on a real rendering for each loop, and with a scanning algorithm
    # like this it can last minutes…

    adjoining_margins = []
    current_position_y = box.content_box_y()
    new_children = []
    for column_children_or_block in columns_and_blocks:
        if not isinstance(column_children_or_block, list):
            # We get a spanning block, we display it like other blocks.
            block = column_children_or_block
            resolve_percentages(block, containing_block)
            block.position_x = box.content_box_x()
            block.position_y = current_position_y
            new_child, _, _, adjoining_margins, _ = block_level_layout(
                context, block, original_max_position_y, skip_stack,
                containing_block, page_is_empty, absolute_boxes, fixed_boxes,
                adjoining_margins)
            new_children.append(new_child)
            current_position_y = (
                new_child.border_height() + new_child.border_box_y())
            adjoining_margins.append(new_child.margin_bottom)
            continue

        excluded_shapes = context.excluded_shapes[:]

        # We have a list of children that we have to balance between columns.
        column_children = column_children_or_block

        # Find the total height of the content
        current_position_y += collapse_margin(adjoining_margins)
        adjoining_margins = []
        column_box = create_column_box(column_children)
        new_child, _, _, _, _ = block_box_layout(
            context, column_box, float('inf'), skip_stack, containing_block,
            page_is_empty, [], [], [])
        height = new_child.margin_height()
        total_height = height
        if style['column_fill'] == 'balance':
            height /= count

        # Try to render columns until the content fits, increase the column
        # height step by step by binary search limits.

        # helper to derive the step_size
        def step_size_calc(value):
            return max(1, value)
            # coercing to power of 2 has no benefit, but increases number of steps..
            # result = round(value).bit_length()
            # return 1 if result == 0 else 1 << result-1

        # difference between upper and lower height is the current search step size
        # start value is arbitrary height / 4
        step_size = step_size_calc((height)/4)
        lower_height = height
        upper_height = 0
        # while the right height has not been found
        while True:
            column_skip_stack = skip_stack
            # Remove extra excluded shapes introduced during previous loop
            new_excluded_shapes = (
                len(context.excluded_shapes) - len(excluded_shapes))
            for i in range(new_excluded_shapes):
                context.excluded_shapes.pop()

            # through all columns
            for i in range(count):
                # render the column.
                new_box, resume_at, next_page, _, _ = block_box_layout(
                    context, column_box, box.content_box_y() + height,
                    column_skip_stack, containing_block, page_is_empty,
                    [], [], [])

                # did we render anything?
                if new_box is None:
                    # Give up and use the total content height.
                    height = total_height
                    break

                # render of the next column shall pickup where this one left
                column_skip_stack = resume_at

                # Stop if we already rendered the whole content
                if resume_at is None:
                    break

            # gave up or reached the total_height of all content combined?
            if height >= total_height:
                break

            # rendered the whole content?
            if column_skip_stack is None:
                if step_size == 1:
                    break
                else:
                    # found a working height, but our binary step is still to big.
                    # need to continue and check if height is lowest acceptable
                    upper_height = height
                    # we need to step backwards until our stepsize is 1.
                    step_size = step_size_calc((upper_height-lower_height)/2)
                    height -= step_size
            else:
                # overall height was not enough to fit the whole content =>

                # height value itself is not acceptable - height+1 might be
                lower_height = height+1
                
                # if a real upper limit is not known. we do not half the stepsize
                # Increase the columns heights and render them once again
                if not upper_height == 0:
                    step_size = step_size_calc((upper_height-lower_height)/2)
                    height = min(height+step_size, upper_height)
                    # optimization: avoid last block_box_layout if we already know that our new height is acceptable
                    if step_size == 1 and height == upper_height:
                        break
                else:
                    height = height+step_size
                

My question is: Why is the height information of each child - as is used to determine the total content height - not enough to fill the children into columns as they fit? Why call block_box_layout in every iteration of the height scan?

Hope your pdf-backend migration is progressing well!

Johannes

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3 participants